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CR Analysis

by gauravgundal » Tue Jun 15, 2010 5:00 pm
Good morning experts :

I have some something to ask about the C.R,specially weakening the Conclusion.I have seen argument with conclusion saying "If X happens ,y will happen " for weakening this argument we just have to find answer that y will never happen and that y is independent of X.

Please let me know if I am correct.


Second : Conclusion states that "sam is smart because sam's family is smart"
for weakening this one if I try to find the answer which makes the above reason i;e., sam's family is smart ,invalid the argument will fall

Please let me know if i am correct
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by kvcpk » Tue Jun 15, 2010 9:19 pm
if x happens, y will happen means to say,
x->y
to weaken it we need to show that ~y->~x
so we need to show that y will not happen. SO x did not happen

Experts - correct me if i am wrong.

Can you explain the below statement again?
gauravgundal wrote: Second : Conclusion states that "sam is smart because sam's family is smart"
for weakening this one if I try to find the answer which makes the above reason i;e., sam's family is smart ,invalid the argument will fall
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by lunarpower » Wed Jun 16, 2010 12:17 am
nope, this is incorrect.

actually, the negation of "if x then y" is "it is possible that/there are instances of x AND NOT y".

if you apply this to a real-life situation, it will actually become fairly obvious. for instance, consider the following statement:
all models are tall and skinny.
(in if-then form, this is if someone is a model, then he/she is tall and skinny.)
the negation of this statement is "there is a model / are models who are NOT tall and skinny" (i.e., "x but not y", where x = model and y = tall/skinny).

so, therefore, the only way that you can really weaken a statement of the form "if x, then y" is to find an example of something that is "x" but NOT "y".
for weakening this argument we just have to find answer that y will never happen
although such an answer might have utility in terms of weakening the argument, there's just no way you would ever see something like this -- it's much too extreme.
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by lunarpower » Wed Jun 16, 2010 12:20 am
kvcpk wrote:if x happens, y will happen means to say,
x->y
to weaken it we need to show that ~y->~x
so we need to show that y will not happen. SO x did not happen

Experts - correct me if i am wrong.
whoa, no.

in fact, "if NOT y, then NOT x" is equivalent to "if x, then y" -- i.e., they are essentially two versions of the same statement!
i.e., if you have a statement that "not y --> not x", then this statement actually PROVES that "x --> y"; the two are absolutely equivalent statements.

ex:
consider the example in the post above this one.
if i give you a statement that says "if someone is NOT tall and skinny, then he/she is NOT a model", then this statement actually proves the truth of "if someone is a model, then he/she must be tall and skinny".
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by gauravgundal » Wed Jun 16, 2010 4:34 pm
I have found two O.G weakening C.R problems
OG 12 Prb no 23 ,in which the conclusion is "if production of the drug continues --> the ibora tree will become extinct."
and the correct answer says "The ibora will not become extinct" that means it's "not Y" for [if x ,then Y]


OG 12 Prb no 40 ,in which the conclusion says
Coffee Awareness --> Reduction in Coffee consumption

The correct answer says "Z [Increase in coffee price] caused Reduction in coffee consumption"
the format becomes [if not x,then y] would be correct in this case.

Please correct me if I am wrong.
Am I doing some wrong analysis?
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by lunarpower » Thu Jun 17, 2010 2:57 am
gauravgundal wrote:I have found two O.G weakening C.R problems
OG 12 Prb no 23 ,in which the conclusion is "if production of the drug continues --> the ibora tree will become extinct."
and the correct answer says "The ibora will not become extinct" that means it's "not Y" for [if x ,then Y]
hmm? that's not what the correct answer says, at least not in my og12. does yours really *say* those actual words?

the correct answer (which i'm not allowed to cite in its entirety) gives a feasible means of producing the ibora without its going extinct, i.e., an example of X that is not Y.
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by lunarpower » Thu Jun 17, 2010 2:58 am
OG 12 Prb no 40
oh. yeah, this is a different sort of thing.
this argument's conclusion is not just a simple if/then statement; it's a statement of CAUSATION. i.e., it is actually saying that x CAUSES y.
this is much more specific, and much narrower, than "if x, then y".

more to the point:
if two things X and Y are correlated, then any of the following could be the root of the correlation:
1) X causes Y
2) Y causes X
3) some other factor (Z) causes these things, and the correlation of X and Y is thus coincidental rather than causal

in og12 #40, the argument says (1), but choice e says (3).

notice that ALL THREE of the above possibilities are entirely consistent with "if x, then y" (and also with "if y, then x"), so the above considerations of logic aren't helpful here.
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by sohrabkalra » Tue Dec 13, 2011 5:54 am
my doubt in the above problem (Q:40 Og12) is that the premise nowhere says
a) That some other factor(Z) actually causes it. It just says that Z(increases price) happens, it leaves it to assume that happening of Z has a definite impact on X(reduced consumption). It might be the case purchasing power also increases and Z has no effect at all ? Although it appears justifiable to accept this choice according to common sense but it requires assuming

c) whereas in the choice C in that problem , it refrains us from assuming that all types of coffee have caffiene(which is justifiably assumable as is the assumption in E). If we assume that all type of coffee have caffiene , then this statement clearly destroys the cause-effect relation by suggesting there is DEFINITELY some other reason.

Would be great if you could point out the error in my reasoning . Or is it picking the best out of 2?
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